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Revered for its translucent quality, hard-paste porcelain was originally made from a mixture of kaolin, a soft white clay, and feldspathic rock fired at a temperature around 2,650 degrees Fahrenheit — a recipe that, starting in the 16th century, European potters obsessively tried and failed to master.

It occurs in the various feldspars and feldspathic rocks, and in mica.

However, the English bone porcelains are very beautiful, and though they are not genuine feldspathic products they are highly esteemed and in demand everywhere.

Personally I prefer it to a pure feldspathic china. 

First we have the deluges of submarine lavas, which were poured out long before the Andes lifted their heads above the waters; then alternate porphyritic strata, feldspathic streams, and gypseous exhalations; then, at a later day, floods of basaltic lava; next the old tertiary eruptions; and, lastly, the vast accumulations of boulders, gravel, ashes, pumice, and mud of the present day, spread over the Valley of Quito and the west slope of the Cordilleras to an unknown depth beneath the sea.